Method for treating arrhythmias

ABSTRACT

Methods are provided for treating arrhythmia in a manner that minimizes undesirable side effects, comprising administration of a therapeutically effective minimal dose of an A 1  adenosine receptor agonist with a therapeutically effective minimal dose of a beta blocker, calcium channel blocker, or a cardiac glycoside.

Priority is claimed to U.S. Provisional Patent Application Ser. No.60/373,766, filed Apr. 18, 2002, the complete disclosure of which ishereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a method of treating arrhythmias and heartfailure in a manner that minimizes undesirable side effects, comprisingadministration of a low dose of an adenosine A₁ receptor agonist inconjunction with a low dose of a beta blocker, or a calcium channelblocker, or a cardiac glycoside.

BACKGROUND INFORMATION

Arrhythmias are abnormal heart rhythms that occur either in the atria orthe ventricles. Arrhythmias arising in the atria are called atrialarrhythmias, and these disorders include atrial fibrillation, atrialflutter, and paroxysmal atrial tachycardia (PSVT). Arrhythmias arisingin the ventricles, known as ventricular arrhythmias, are a group ofdisorders having diverse etiologies, including idiopathic ventriculartachycardia, ventricular fibrillation, and Torsade de Pointes (TdP).Arrhythmias can range from incidental, asymptomatic clinical findings tolife-threatening abnormalities, and account for a significant percentageof the causes of death in humans. Thus, it is desirable to developmethods of mitigating the effects of arrhythmias.

A variety of anti-arrhythmic drug therapies are presently available, andare classified as follows. Class I anti-arrhythmics, comprising sodiumchannel blockers; Class II, comprising beta-blockers; Class III,comprising drugs that prolong action potential (usually by blockingpotassium channels); and Class IV, comprising calcium channels blockers.Cardiac glycosides, for example digitalis, are also used as drugs forthe treatment of arrhythmia, but they have a delayed onset of action(about 30 minutes) and their peak effects are not observed for ≧3 to 4hours after administration. Additionally, digitalis is toxic at dosesclose to the therapeutic dose, which limits the utility of the compound.

In fact all of the above classes have significant limitations. Forexample, beta-blockers, such as propranolol and esmolol, andcalcium-channel blockers, for example verapamil, bepridil, anddiltiazem, can cause hypotension, potentially have negative inotropiceffects, and may also precipitate new arrhythmias, including TdP.

Adenosine, which is widely found in nature, is another compound that hasanti-arrhythmic activities, by virtue of its ability, at certain doselevels, to slow the conduction in the atrioventricular node. Theanti-arrhythmic effects of adenosine are due exclusively to itsinteraction with the adenosine A₁ receptor subtype. However, althoughadenosine is highly effective in ameliorating arrhythmia, it also bindscontemporaneously to other adenosine receptor subtypes (A_(2A), A_(2B),and A₃), which results in undesirable side effects, such asvasodilation, changes in the heart rate, mast cell degradation, etc.Adenosine also has a short half-life (˜10 sec), making it ineffective intreating conditions that require prolonged action.

Compounds that are selective agonists for adenosine A₁ receptors areknown. For example, a new class of agonists that bind to adenosine A₁receptors and that are useful in treating arrhythmias are disclosed inU.S. Pat. No. 5,789,416, and in U.S. patent application Ser. No.10/194,335, the entire disclosures of which are hereby incorporated byreference. These compounds have a high specificity for the adenosine A₁receptor subtype, but like all therapeutic compounds, can potentiallycause side effects.

Antiarrythymic agents in general have a narrow margin between the doserequired to produce the desired antiarrhythmic effect and the dose thatproduces an adverse effect. It would therefore be desirable to find amethod of treating arrhythmia that is effective at low doses (or minimaldoses) of the active agent, thus decreasing the likelihood of adverseeffects. We have discovered that low doses of adenosine A₁ receptoragonists, preferably partial agonists, and more preferably selectiveadenosine A₁ receptor agonists, can be used in combination with lowdoses of beta blocker, calcium channel blockers, or cardiac glycosides,to provide an effective treatment for arrhythmia that minimizes the sideeffects of beta blockers, calcium channel blockers, cardiac glycosides,and A₁-adenosine receptor agonists that may potentially occur when takenindividually. It has also been observed that at low doses, thecombination of these agents act in a synergistic manner, thus reducingeven further the chance of side effects. It has also been observed thatthe combination of an A₁ adenosine receptor antagonist with a betablocker can be used in the treatment of heart failure, includingischemic heart disease, congestive heart failure, heart failuresyndrome, hypertension, and the like.

Accordingly, a novel and effective method of treating arrhythmias isprovided that restores sinus rhythm without slowing the sinus rate andis virtually free of undesirable side effects, such as changes in meanarterial pressure, blood pressure, increased heart rate, TdP, or otheradverse effects.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an effective method oftreating arrhythmias in a mammal while minimizing undesirable sideeffects. Accordingly, in a first aspect, the invention relates to amethod of treating arrhythmias in a mammal, comprising administration ofa therapeutically effective minimal dose of an A₁ adenosine receptoragonist in conjunction with a therapeutically effective minimal dose ofa beta blocker, calcium channel blocker, or a cardiac glycoside to amammal in need thereof.

In one embodiment, an A₁-adenosine receptor agonist useful for thisinvention is a compound of Formula I:

wherein:

R₁ is an optionally substituted heterocyclic group, preferablymonocyclic. The effective dose is preferably in the range of 0.0001–0.05mg/kg, more preferably 0.0005–0.02 mg/kg.

In a preferred embodiment, R¹ is 3-tetrahydrofuranyl,3-tetrahydrothiofuranyl, 4-pyranyl, or 4-thiopyranyl. The most preferredcompound of Formula I is 6-(3-(R)-N-aminotetrahydrofuranyl)purineriboside (hereinafter referred to as CVT-510).

In another embodiment, an A₁ -adenosine receptor agonist useful for thisinvention is a compound of Formula II:

wherein:

-   R¹ is optionally substituted alkyl, optionally substituted    cycloalkyl, optionally substituted aryl, or optionally substituted    heteroaryl;-   R² is hydrogen, halo, trifluoromethyl, optionally substituted acyl,    or cyano;-   R³ is optionally substituted alkyl, optionally substituted    cycloalkyl, optionally substituted aryl; optionally substituted    heteroaryl, or optionally substituted heterocyclyl,-   R⁴ and R⁵ are independently hydrogen or optionally substituted acyl;    and-   X and Y are independently a covalent bond or optionally substituted    alkylene.    The effective dose is preferably in the range of 0.1 to 200 mg/kg,    more preferably 0.5 to 50 mg/kg.

The most preferred compound of Formula II is one in which R¹ is2-hydroxycyclopentyl, X and Y are covalent bonds, R², R³, and R⁴ arehydrogen, and R⁵ is 2-fluorophenyl, most preferably2-{6-[((1R,2R)-2-hydroxycyclopentyl)amino]purin-9-yl}(4S,5S,3R)-5-[(2-fluorophenylthio)methyl]oxolane-3,4-diol,hereinafter referred to as CVT-3619.

Preferred beta blockers include atenolol, esmolol, sotalol, andpropranolol. More preferred is esmolol. The preferred effective dose isin the range of 0.01 to 100 mg/kg, more preferably in the range of 0.1to 10 mg/kg.

Preferred calcium channel blockers include amlodipine, bepridil,diltiazem, felodipine, isradipine, nicardipine, nifedipine, nimodipineand verapamil. The preferred effective dose is in the range of 0.01 to50 mg/kg, more preferably in the range of 0.1 to 10 mg/kg.

Preferred cardiac glycosides include digoxin and digitoxin.

One preferred embodiment of the invention is a method of treatingarrhythmias in a mammal comprising administering a therapeuticallyeffective minimal dose of CVT-510 in conjunction with a therapeuticallyeffective minimal dose of a beta blocker, preferably esmolol, atenolol,sotolol or propranol, more preferably esmolol, to a mammal in needthereof.

Another preferred embodiment of the invention is a method of treatingarrhythmias in a mammal comprising administering a therapeuticallyeffective minimal dose of CVT-3619, and a therapeutically effectiveminimal dose of a beta blocker, preferably esmolol, atenolol, sotolol orpropranol, more preferably esmolol, to a mammal in need thereof.

Another preferred embodiment of the invention is a method of treatingarrhythmias in a mammal comprising administering a therapeuticallyeffective minimal dose of CVT-510, or a therapeutically effectiveminimal dose of CVT-3619, in conjunction with a therapeuticallyeffective minimal dose of a calcium channel blocker, preferablyverapamil, to a mammal in need thereof.

A third preferred embodiment of the invention is a method of treatingarrhythmias in a mammal comprising administering a therapeuticallyeffective minimal dose of CVT-510, or a therapeutically effectiveminimal dose of CVT-3619, in conjunction with a therapeuticallyeffective minimal dose of a cardiac glycoside, preferably digoxin, to amammal in need thereof.

In another aspect, the invention relates to a pharmaceutical compositionuseful for treating arrhythmias in a mammal, comprising atherapeutically effective minimal dose of an A₁ adenosine receptoragonist and a therapeutically effective minimal dose of a beta blocker,and at least one pharmaceutically acceptable excipient.

One preferred embodiment of the invention is a pharmaceuticalcomposition for treating arrhythmias in a mammal, comprising atherapeutically effective minimal dose of a compound of Formula I, morepreferably CVT-510, and a therapeutically effective minimal dose of abeta blocker, preferably esmolol, atenolol, sotolol or propranol, morepreferably esmolol, to a mammal in need thereof. The Formula I dose ispreferably in the range of 0.0001–0.05 mg/kg, more preferably0.0005–0.02 mg/kg, and the beta blocker dose is in the in the range of0.01 to 100 mg/kg, more preferably in the range of 0.1 to 10 mg/kg.

Another preferred embodiment of the invention is a pharmaceuticalcomposition for treating arrhythmias in a mammal, comprising atherapeutically effective minimal dose of a compound of Formula II, morepreferably CVT-3619, and a therapeutically effective minimal dose of abeta blocker, preferably esmolol, atenolol, sotolol or propranol, morepreferably esmolol, to a mammal in need thereof. The dose is preferablyin the range of 0.1 to 200 mg/kg, more preferably 0.5 to 25 mg/kg, andthe beta blocker dose is in the in the range of 0.01 to 100 mg/kg, morepreferably in the range of 0.1 to 10 mg/kg.

In another aspect, the invention relates to a method of treating heartfailure in a mammal, comprising administration of a therapeuticallyeffective minimal dose of an A₁ adenosine receptor agonist inconjunction with a therapeutically effective minimal dose of a betablocker to a mammal in need thereof.

DESCRIPTION OF FIGURES

FIG. 1. Comparison of the effect of CVT-3619 alone and CVT-3619 incombination with propranolol on heart rate.

FIG. 2. Comparison of the effect of CVT-3619 alone and CVT-3619 incombination with propranolol on heart rate.

FIG. 3. Comparison of the effect of 20 μg/kg of CVT-510, 10 mg/kg ofesmolol, and a combination of 20 μg/kKg of CVT-510 and 10 mg/kg ofesmolol on heart rate.

FIG. 4. Comparison of the effect of 20 μg/kg of CVT-510, 3 mg/kg ofesmolol, and a combination of 20 μg/kg of CVT-510 and 3 mg/kg of esmololon heart rate.

FIG. 5. Comparison of the effect of 10 μg/kg, 20 μg/Kg and 30 μg/kgdoses of CVT-510, 1 mk/kg and 3 mg/kg of esmolol, and a combination of20 μg/kg of CVT-510 and 1 and 3 mg/kg of esmolol on duration ofBradycardia.

FIG. 6. Comparison of plasma levels of CVT-510 alone and a combinationof CVT-510 and metoprolol.

FIG. 7. Dose response curve for metoprolol in the absence and presenceof CVT-510.

FIG. 8. This figure represents the data shown in FIG. 7.

FIG. 9. Effect of CVT-510 (0.5 μg/kg) and metoprolol (0.1 mg/kg), whichwere given as an iv bolus, on PR interval

FIG. 10. Effect of CVT-510 (0.5 μg/kg) and esmolol on PR interval

ABBREVIATIONS

-   BPM: beats per minute-   HR: Heart rate-   SH: Stimulus to His (length of time for conduction of current    through AV node)-   PSVT Paroxysmal Atrial Tachycardia    Definitions and General Parameters

As used in the present specification, the following words and phrasesare generally intended to have the meanings as set forth below, exceptto the extent that the context in which they are used indicatesotherwise.

The term “alkyl” refers to a monoradical branched or unbranchedsaturated hydrocarbon chain having from 1 to 20 carbon atoms. This termis exemplified by groups such as methyl, ethyl, n-propyl, iso-propyl,n-butyl, iso-butyl, t-butyl, n-hexyl,n-decyl, tetradecyl, and the like.

The term “substituted alkyl” refers to:

-   1) an alkyl group as defined above, having from 1 to 5 substituents,    preferably 1 to 3 substituents, selected from the group consisting    of alkenyl, alkynyl, alkoxy, cycloalkyl, cycloalkenyl, acyl,    acylamino, acyloxy, amino, aminocarbonyl, alkoxycarbonylamino,    azido, cyano, halogen, hydroxy, keto, thiocarbonyl, carboxy,    carboxyalkyl, arylthio, heteroarylthio, heterocyclylthio, thiol,    alkylthio, aryl, aryloxy, heteroaryl, aminosulfonyl,    aminocarbonylamino, heteroaryloxy, heterocyclyl, heterocyclooxy,    hydroxyamino, alkoxyamino, nitro, —SO-alkyl, —SO-aryl,    —SO-heteroaryl, —SO₂-alkyl, SO₂-aryl and —SO₂-heteroaryl. Unless    otherwise constrained by the definition, all substituents may be    optionally further substituted by alkyl, alkoxy, halogen, CF₃,    amino, substituted amino, cyano, or —S(O)_(n)R, in which R is alkyl,    aryl, or heteroaryl and n is 0, 1 or 2; or-   2) an alkyl group as defined above that is interrupted by 1–5 atoms    or groups independently chosen from oxygen, sulfur and —NR_(a)—,    where R_(a) is chosen from hydrogen, alkyl, cycloalkyl, alkenyl,    cycloalkenyl, alkynyl, aryl, heteroaryl and heterocyclyl. All    substituents may be optionally further substituted by alkyl, alkoxy,    halogen, CF₃, amino, substituted amino, cyano, or —S(O)_(n)R, in    which R is alkyl, aryl, or heteroaryl and n is 0, 1 or 2; or-   3) an alkyl group as defined above that has both from 1 to 5    substituents as defined above and is also interrupted by 1–5 atoms    or groups as defined above. The term “lower alkyl” refers to a    monoradical branched or unbranched saturated hydrocarbon chain    having from 1 to 6 carbon atoms. This term is exemplified by groups    such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl,    t-butyl, n-hexyl, and the like.

The term “substituted lower alkyl” refers to lower alkyl as definedabove having 1 to 5 substituents, preferably 1 to 3 substituents, asdefined for substituted alkyl, or a lower alkyl group as defined abovethat is interrupted by 1–5 atoms as defined for substituted alkyl, or alower alkyl group as defined above that has both from 1 to 5substituents as defined above and is also interrupted by 1–5 atoms asdefined above.

The term “alkylene” refers to a diradical of a branched or unbranchedsaturated hydrocarbon chain, preferably having from 1 to 20 carbonatoms, preferably 1–10 carbon atoms, more preferably 1–6 carbon atoms.This term is exemplified by groups such as methylene (—CH₂—), ethylene(—CH₂CH₂—), the propylene isomers (e.g., —CH₂CH₂CH₂— and —CH(CH₃)CH₂—)and the like.

The term “lower alkylene” refers to a diradical of a branched orunbranched saturated hydrocarbon chain, preferably having from 1 to 6carbon atoms.

The term “substituted alkylene” refers to:

-   (1) an alkylene group as defined above having from 1 to 5    substituents selected from the group consisting of alkyl, alkenyl,    alkynyl, alkoxy, cycloalkyl, cycloalkenyl, acyl, acylamino, acyloxy,    amino, aminocarbonyl, alkoxycarbonylamino, azido, cyano, halogen,    hydroxy, keto, thiocarbonyl, carboxy, carboxyalkyl, arylthio,    heteroarylthio, heterocyclylthio, thiol, alkylthio, aryl, aryloxy,    heteroaryl, aminosulfonyl, aminocarbonylamino, heteroaryloxy,    heterocyclyl, heterocyclooxy, hydroxyamino, alkoxyamino, nitro,    —SO-alkyl, —SO-aryl, —SO-heteroaryl, —SO₂-alkyl, SO₂-aryl and    —SO₂-heteroaryl. Unless otherwise constrained by the definition, all    substituents may be optionally further substituted by alkyl, alkoxy,    halogen, CF₃, amino, substituted amino, cyano, or —S(O)_(n)R, in    which R is alkyl, aryl, or heteroaryl and n is 0, 1 or 2; or-   (2) an alkylene group as defined above that is interrupted by 1–5    atoms or groups independently chosen from oxygen, sulfur and    NR_(a)—, where R_(a) is chosen from hydrogen, optionally substituted    alkyl, cycloalkyl, cycloalkenyl, aryl, heteroaryl and heterocycyl,    or groups selected from carbonyl, carboxyester, carboxyamide and    sulfonyl; or-   (3) an alkylene group as defined above that has both from 1 to 5    substituents as defined above and is also interrupted by 1–20 atoms    as defined above. Examples of substituted alkylenes are    chloromethylene (—CH(Cl)—), aminoethylene (—CH(NH₂)CH₂—),    methylaminoethylene (—CH(NHMe)CH₂—), 2-carboxypropylene isomers    (—CH₂CH(CO₂H)CH₂—), ethoxyethyl (—CH₂CH₂O—CH₂CH₂—),    ethylmethylaminoethyl (—CH₂CH₂N(CH₃)CH₂CH₂—),    1-ethoxy-2-(2-ethoxy-ethoxy)ethane    (—CH₂CH₂O—CH₂CH₂—OCH₂CH₂—OCH₂CH₂—), and the like.

The term “aralkyl: refers to an aryl group covalently linked to analkylene group, where aryl and alkylene are defined herein. “Optionallysubstituted aralkyl” refers to an optionally substituted aryl groupcovalently linked to an optionally substituted alkylene group. Sucharalkyl groups are exemplified by benzyl, phenylethyl,3-(4-methoxyphenyl)propyl, and the like.

The term “alkoxy” refers to the group R—O—, where R is optionallysubstituted alkyl or optionally substituted cycloalkyl, or R is a group—Y-Z, in which Y is optionally substituted alkylene and Z is; optionallysubstituted alkenyl, optionally substituted alkynyl; or optionallysubstituted cycloalkenyl, where alkyl, alkenyl, alkynyl, cycloalkyl andcycloalkenyl are as defined herein. Preferred alkoxy groups are alkyl-O—and include, by way of example, methoxy, ethoxy, n-propoxy, iso-propoxy,n-butoxy, tert-butoxy, sec-butoxy, n-pentoxy, n-hexoxy,1,2-dimethylbutoxy, and the like.

The term “alkylthio” refers to the group R—S—, where R is as defined foralkoxy.

The term “alkenyl” refers to a monoradical of a branched or unbranchedunsaturated hydrocarbon group preferably having from 2 to 20 carbonatoms, more preferably 2 to 10 carbon atoms and even more preferably 2to 6 carbon atoms and having 1–6, preferably 1, double bond (vinyl).Preferred alkenyl groups include ethenyl or vinyl (—CH═CH₂), 1-propyleneor allyl (—CH₂CH═CH₂), isopropylene (—C(CH₃)═CH₂),bicyclo[2.2.1]heptene, and the like. In the event that alkenyl isattached to nitrogen, the double bond cannot be alpha to the nitrogen.

The term “lower alkenyl” refers to alkenyl as defined above having from2 to 6 carbon atoms.

The term “substituted alkenyl” refers to an alkenyl group as definedabove having from 1 to 5 substituents, and preferably 1 to 3substituents, selected from the group consisting of alkyl, alkenyl,alkynyl, alkoxy, cycloalkyl, cycloalkenyl, acyl, acylamino, acyloxy,amino, aminocarbonyl, alkoxycarbonylamino, azido, cyano, halogen,hydroxy, keto, thiocarbonyl, carboxy, carboxyalkyl, arylthio,heteroarylthio, heterocyclylthio, thiol, alkylthio, aryl, aryloxy,heteroaryl, aminosulfonyl, aminocarbonylamino, heteroaryloxy,heterocyclyl, heterocyclooxy, hydroxyamino, alkoxyamino, nitro,—SO-alkyl, —SO-aryl, —SO-heteroaryl, —SO₂-alkyl, SO₂-aryl and—SO₂-heteroaryl. All substituents may be optionally further substitutedby alkyl, alkoxy, halogen, CF₃, amino, substituted amino, cyano, or—S(O)_(n)R, in which R is alkyl, aryl, or heteroaryl and n is 0, 1 or 2.

The term “alkynyl” refers to a monoradical of an unsaturatedhydrocarbon, preferably having from 2 to 20 carbon atoms, morepreferably 2 to 10 carbon atoms and even more preferably 2 to 6 carbonatoms and having at least 1 and preferably from 1–6 sites of acetylene(triple bond) unsaturation. Preferred alkynyl groups include ethynyl,(—C≡CH), propargyl (or propynyl, —C≡CCH₃), and the like. In the eventthat alkynyl is attached to nitrogen, the triple bond cannot be alpha tothe nitrogen.

The term “substituted alkynyl” refers to an alkynyl group as definedabove having from 1 to 5 substituents, and preferably 1 to 3substituents, selected from the group consisting of alkyl, alkenyl,alkynyl, alkoxy, cycloalkyl, cycloalkenyl, acyl, acylamino, acyloxy,amino, aminocarbonyl, alkoxycarbonylamino, azido, cyano, halogen,hydroxy, keto, thiocarbonyl, carboxy, carboxyalkyl, arylthio,heteroarylthio, heterocyclylthio, thiol, alkylthio, aryl, aryloxy,heteroaryl, aminosulfonyl, aminocarbonylamino, heteroaryloxy,heterocyclyl, heterocyclooxy, hydroxyamino, alkoxyamino, nitro,—SO-alkyl, —SO-aryl, —SO-heteroaryl, —SO₂-alkyl, SO₂-aryl and—SO₂-heteroaryl. All substituents may be optionally further substitutedby alkyl, alkoxy, halogen, CF₃, amino, substituted amino, cyano, or—S(O)_(n)R, in which R is alkyl, aryl, or heteroaryl and n is 0, 1 or 2.

The term “aminocarbonyl” refers to the group —C(O)NRR where each R isindependently hydrogen, alkyl, aryl, heteroaryl, heterocyclyl or whereboth R groups are joined to form a heterocyclic group (e.g.,morpholino). All substituents may be optionally further substituted byalkyl, alkoxy, halogen, CF₃, amino, substituted amino, cyano, or—S(O)_(n)R, in which R is alkyl, aryl, or heteroaryl and n is 0, 1 or 2.

The term “acylamino” refers to the group —NRC(O)R where each R isindependently hydrogen, alkyl, aryl, heteroaryl, or heterocyclyl. Allsubstituents may be optionally further substituted by alkyl, alkoxy,halogen, CF₃, amino, substituted amino, cyano, or —S(O)_(n)R, in which Ris alkyl, aryl, or heteroaryl and n is 0, 1 or 2.

The term “acyloxy” refers to the groups —O(O)C-alkyl, —O(O)C-cycloalkyl,—O(O)C-aryl, —O(O)C-heteroaryl, and —O(O)C-heterocyclyl. Allsubstituents may be optionally further substituted by alkyl, alkoxy,halogen, CF₃, amino, substituted amino, cyano, or —S(O)_(n)R, in which Ris alkyl, aryl, or heteroaryl and n is 0, 1 or 2.

The term “aryl” refers to an aromatic carbocyclic group of 6 to 20carbon atoms having a single ring (e.g., phenyl) or multiple rings(e.g., biphenyl), or multiple condensed (fused) rings (e.g., naphthyl oranthryl). Preferred aryls include phenyl, naphthyl and the like.

Unless otherwise constrained by the definition for the aryl substituent,such aryl groups can optionally be substituted with from 1 to 5substituents, preferably 1 to 3 substituents, selected from the groupconsisting of alkyl, alkenyl, alkynyl, alkoxy, cycloalkyl, cycloalkenyl,acyl, acylamino, acyloxy, amino, aminocarbonyl, alkoxycarbonylamino,azido, cyano, halogen, hydroxy, keto, thiocarbonyl, carboxy,carboxyalkyl, arylthio, heteroarylthio, heterocyclylthio, thiol,alkylthio, aryl, aryloxy, heteroaryl, aminosulfonyl, aminocarbonylamino,heteroaryloxy, heterocyclyl, heterocyclooxy, hydroxyamino, alkoxyamino,nitro, —SO-alkyl, —SO-aryl, —SO-heteroaryl, —SO₂-alkyl, SO₂-aryl and—SO₂-heteroaryl. All substituents may be optionally further substitutedby alkyl, alkoxy, halogen, CF₃, amino, substituted amino, cyano, or—S(O)_(n)R, in which R is alkyl, aryl, or heteroaryl and n is 0, 1 or 2.

The term “aryloxy” refers to the group aryl-O— wherein the aryl group isas defined above, and includes optionally substituted aryl groups asalso defined above. The term “arylthio” refers to the group R—S—, whereR is as defined for aryl.

The term “amino” refers to the group —NH₂.

The term “substituted amino” refers to the group —NRR where each R isindependently selected from the group consisting of hydrogen, alkyl,cycloalkyl, carboxyalkyl (for example, benzyloxycarbonyl), aryl,heteroaryl and heterocyclyl provided that both R groups are nothydrogen, or a group —Y-Z, in which Y is optionally substituted alkyleneand Z is alkenyl, cycloalkenyl, or alkynyl. All substituents may beoptionally further substituted by alkyl, alkoxy, halogen, CF₃, amino,substituted amino, cyano, or —S(O)_(n)R, in which R is alkyl, aryl, orheteroaryl and n is 0, 1 or 2.

The term “carboxyalkyl” refers to the groups —C(O)O-alkyl,—C(O)O-cycloalkyl, where alkyl and cycloalkyl, are as defined herein,and may be optionally further substituted by alkyl, alkenyl, alkynyl,alkoxy, halogen, CF₃, amino, substituted amino, cyano, or —S(O)_(n)R, inwhich R is alkyl, aryl, or heteroaryl and n is 0, 1 or 2.

The term “cycloalkyl” refers to cyclic alkyl groups of from 3 to 20carbon atoms having a single cyclic ring or multiple condensed rings.Such cycloalkyl groups include, by way of example, single ringstructures such as cyclopropyl, cyclobutyl, cyclopentyl, cyclooctyl, andthe like, or multiple ring structures such as adamantanyl, andbicyclo[2.2.1]heptane, or cyclic alkyl groups to which is fused an arylgroup, for example indan, and the like.

The term “substituted cycloalkyl” refers to cycloalkyl groups havingfrom 1 to 5 substituents, and preferably 1 to 3 substituents, selectedfrom the group consisting of alkyl, alkenyl, alkynyl, alkoxy,cycloalkyl, cycloalkenyl, acyl, acylamino, acyloxy, amino,aminocarbonyl, alkoxycarbonylamino, azido, cyano, halogen, hydroxy,keto, thiocarbonyl, carboxy, carboxyalkyl, arylthio, heteroarylthio,heterocyclylthio, thiol, alkylthio, aryl, aryloxy, heteroaryl,aminosulfonyl, aminocarbonylamino, heteroaryloxy, heterocyclyl,heterocyclooxy, hydroxyamino, alkoxyamino, nitro, —SO-alkyl, —SO-aryl,—SO-heteroaryl, —SO₂-alkyl, SO₂-aryl and —SO₂-heteroaryl. Allsubstituents may be optionally further substituted by alkyl, alkoxy,halogen, CF₃, amino, substituted amino, cyano, or —S(O)_(n)R, in which Ris alkyl, aryl, or heteroaryl and n is 0, 1 or 2.

The term “halogen” or “halo” refers to fluoro, bromo, chloro, and iodo.

The term “acyl” denotes a group —C(O)R, in which R is hydrogen,optionally substituted alkyl, optionally substituted cycloalkyl,optionally substituted heterocyclyl, optionally substituted aryl, andoptionally substituted heteroaryl.

The term “heteroaryl” refers to an aromatic group (i.e., unsaturated)comprising 1 to 15 carbon atoms and 1 to 4 heteroatoms selected fromoxygen, nitrogen and sulfur within at least one ring.

Unless otherwise constrained by the definition for the heteroarylsubstituent, such heteroaryl groups can be optionally substituted with 1to 5 substituents, preferably 1 to 3 substituents selected from thegroup consisting of alkyl, alkenyl, alkynyl, alkoxy, cycloalkyl,cycloalkenyl, acyl, acylamino, acyloxy, amino, aminocarbonyl,alkoxycarbonylamino, azido, cyano, halogen, hydroxy, keto, thiocarbonyl,carboxy, carboxyalkyl, arylthio, heteroarylthio, heterocyclylthio,thiol, alkylthio, aryl, aryloxy, heteroaryl, aminosulfonyl,aminocarbonylamino, heteroaryloxy, heterocyclyl, heterocyclooxy,hydroxyamino, alkoxyamino, nitro, —SO-alkyl, —SO-aryl, —SO-heteroaryl,—SO₂-alkyl, SO₂-aryl and —SO₂-heteroaryl. All substituents may beoptionally further substituted by alkyl, alkoxy, halogen, CF₃, amino,substituted amino, cyano, or —S(O)_(n)R, in which R is alkyl, aryl, orheteroaryl and n is 0, 1 or 2. Such heteroaryl groups can have a singlering (e.g., pyridyl or furyl) or multiple condensed rings (e.g.,indolizinyl, benzothiazole, or benzothienyl). Examples of nitrogenheterocycles and heteroaryls include, but are not limited to, pyrrole,imidazole, pyrazole, pyridine, pyrazine, pyrimidine, pyridazine,indolizine, isoindole, indole, indazole, purine, quinolizine,isoquinoline, quinoline, phthalazine, naphthylpyridine, quinoxaline,quinazoline, cinnoline, pteridine, carbazole, carboline, phenanthridine,acridine, phenanthroline, isothiazole, phenazine, isoxazole,phenoxazine, phenothiazine, imidazolidine, imidazoline, and the like aswell as N-alkoxy-nitrogen containing heteroaryl compounds.

The term “heteroaryloxy” refers to the group heteroaryl-O—.

The term “heterocyclyl” refers to a monoradical saturated or partiallyunsaturated group having a single ring or multiple condensed rings,having from 1 to 40 carbon atoms and from 1 to 10 hetero atoms,preferably 1 to 4 heteroatoms, selected from nitrogen, sulfur,phosphorus, and/or oxygen within the ring.

Unless otherwise constrained by the definition for the heterocyclicsubstituent, such heterocyclic groups can be optionally substituted with1 to 5, and preferably 1 to 3 substituents, selected from the groupconsisting of alkyl, alkenyl, alkynyl, alkoxy, cycloalkyl, cycloalkenyl,acyl, acylamino, acyloxy, amino, aminocarbonyl, alkoxycarbonylamino,azido, cyano, halogen, hydroxy, keto, thiocarbonyl, carboxy,carboxyalkyl, arylthio, heteroarylthio, heterocyclylthio, thiol,alkylthio, aryl, aryloxy, heteroaryl, aminosulfonyl, aminocarbonylamino,heteroaryloxy, heterocyclyl, heterocyclooxy, hydroxyamino, alkoxyamino,nitro, —SO-alkyl, —SO-aryl, —SO-heteroaryl, —SO₂-alkyl, SO₂-aryl and—SO₂-heteroaryl. All substituents may be optionally further substitutedby alkyl, alkoxy, halogen, CF₃, amino, substituted amino, cyano, or—S(O)_(n)R, in which R is alkyl, aryl, or heteroaryl and n is 0, 1 or 2.Heterocyclic groups can have a single ring or multiple condensed rings.Preferred heterocyclics include tetrahydrofuranyl, morpholino,piperidinyl, and the like.

The term “thiol” refers to the group —SH.

The term “substituted alkylthio” refers to the group —S-substitutedalkyl.

The term “heteroarylthiol” refers to the group —S-heteroaryl wherein theheteroaryl group is as defined above including optionally substitutedheteroaryl groups as also defined above.

The term “sulfoxide” refers to a group —S(O)R, in which R is alkyl,aryl, or heteroaryl. “Substituted sulfoxide” refers to a group —S(O)R,in which R is substituted alkyl, substituted aryl, or substitutedheteroaryl, as defined herein.

The term “sulfone” refers to a group —S(O)₂R, in which R is alkyl, aryl,or heteroaryl. “Substituted sulfone” refers to a group —S(O)₂R, in whichR is substituted alkyl, substituted aryl, or substituted heteroaryl, asdefined herein.

The term “keto” refers to a group —C(O)—. The term “thiocarbonyl” refersto a group —C(S)—. The term “carboxy” refers to a group —C(O)—OH.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where said event or circumstance occurs and instances in whichit does not.

The terms “compound of Formula I” and “compound of Formula II” areintended to encompass the compounds of the invention as disclosed, andthe pharmaceutically acceptable salts, pharmaceutically acceptableesters, and prodrugs of such compounds.

The term “therapeutically effective amount” refers to that amount of anactive ingredient (A₁-agonist, beta-blocker, calcium channel blocker,cardiac glycoside) that is sufficient to effect treatment, as definedbelow, when administered to a mammal in need of such treatment. Thetherapeutically effective amount will vary depending upon the subjectand disease condition being treated, the weight and age of the subject,the severity of the disease condition, the manner of administration andthe like, which can readily be determined by a prescribing physician.

The term “therapeutically effective minimal dose” or “low dose” of an A₁adenosine receptor agonist refers to a dose level of an A₁ adenosinereceptor agonist that is generally considered to be below thetherapeutically effective amount as defined above, but is sufficient toprovide effective treatment when administered in conjunction with a“therapeutically effective minimal dose” or “low dose” of a betablocker, calcium channel blocker, or a cardiac glycoside. For example, atherapeutically effective minimal dose of CVT-3619 is one that would notnormally be considered to be useful in the treatment of arrhythmia, butis now found to be useful in the treatment of arrhythmia whenadministered in conjunction with a therapeutically effective minimaldose of a beta blocker, because of the synergistic effect obtained uponcombining an A₁-agonist with a beta blocker. The therapeuticallyeffective minimal dose will vary depending upon the subject and diseasecondition being treated, the weight and age of the subject, the severityof the disease condition, the manner of administration and the like,which can readily be determined by a prescribing physician.

A therapeutically effective minimal dose of an adenosine A₁ receptoragonist is administered “in conjunction with” a therapeuticallyeffective minimal doses of a beta blocker, or a calcium channel blocker,or a cardiac glycoside. In this context, the word “conjunction” meansthat the doses may be administered together at the same time, forexample in a single pill or solution, or administered separately at thesame time, or administered at different times.

The term “treatment” or “treating” means any treatment of a disease in amammal, including:

-   -   (i) preventing the disease, that is, causing the clinical        symptoms of the disease not to develop;    -   (ii) inhibiting the disease, that is, arresting the development        of clinical symptoms; and/or    -   (iii) relieving the disease, that is, causing the regression of        clinical symptoms.

As used herein, the term “agonist” refers to the ability of a compoundto interact with a receptor and evoke a maximal effect. This effect isknown as the intrinsic efficacy. In contrast, “partial agonists”interact with adenosine A₁ receptors but produce a less than maximalresponse.

The term “adenosine A₁ receptor agonist” refers to an agent that bindsto adenosine A₁ receptors thereby producing a negative dromotropiceffect. For example, CVT-3619 is a partial A₁-adenosine receptoragonist—it has a rate dependent effect upon AV nodal conduction. Itincreases AV-node refractoriness, and thus reduces ventricular rateduring atrial tachyarrhythmia. A₁ agonists also act to inhibit therelease of norepinephrine from the pre-synaptic nerve terminal, and toinhibit the uptake of norepinephrine at the post-synaptic nerveterminal.

The term “beta-blocker” refers to an agent that binds to abeta-adrenergic receptor and inhibits the effects of beta-adrenergicstimulation. Beta-blockers increase AV nodal conduction. In addition,Beta-blockers decrease heart rate by blocking the effect ofnorepinephrine on the post synaptic nerve terminal that controls heartrate. Beta blockers also decrease intracellular Ca⁺⁺ overload, whichinhibits after-depolarization mediated automaticity. Examples of betablockers include atenolol, esmolol, sotalol, propranolol, bopindolol,carteolol, oxprenolol, penbutolol, carvedilol, medroxalol, bucindolol,levobunolol, metipranolol, betaxolol, celiprolol, and propafenone.

The term “calcium channel blocker” refers to an agent that blocksvoltage-dependent “L-type calcium channel. They are used in treatment ofheart diseases, including cardiac arrhythmia—they have a rate dependenteffect upon AV nodal conduction. Examples of calcium channel blockersinclude amlodipine, bepridil, diltiazem, felodipine, isradipine,nicardipine, nifedipine, nimodipine and verapamil.

The term “cardiac glycoside” refers to a compound with a steroidalnucleus and a lactone ring, and usually has one or more sugar residues.They are used in treatment of heart diseases, including cardiacarrhythmia—they have a rate dependent effect upon AV nodal conduction.Examples of cardiac glycosides include digoxin and digitoxin.

The term “synergistic” effect means a result produced by a combinationof drugs that is greater than that produced by each drug alone.

In many cases, the compounds of this invention are capable of formingacid and/or base salts by virtue of the presence of amino and/orcarboxyl groups or groups similar thereto. The term “pharmaceuticallyacceptable salt” refers to salts that retain the biologicaleffectiveness and properties of the compounds of Formula I, and whichare not biologically or otherwise undesirable. Pharmaceuticallyacceptable base addition salts can be prepared from inorganic andorganic bases. Salts derived from inorganic bases, include by way ofexample only, sodium, potassium, lithium, ammonium, calcium andmagnesium salts. Salts derived from organic bases include, but are notlimited to, salts of primary, secondary and tertiary amines, such asalkyl amines, dialkyl amines, trialkyl amines, substituted alkyl amines,di(substituted alkyl) amines, tri(substituted alkyl) amines, alkenylamines, dialkenyl amines, trialkenyl amines, substituted alkenyl amines,di(substituted alkenyl) amines, tri(substituted alkenyl) amines,cycloalkyl amines, di(cycloalkyl) amines, tri(cycloalkyl) amines,substituted cycloalkyl amines, disubstituted cycloalkyl amine,trisubstituted cycloalkyl amines, cycloalkenyl amines, di(cycloalkenyl)amines, tri(cycloalkenyl) amines, substituted cycloalkenyl amines,disubstituted cycloalkenyl amine, trisubstituted cycloalkenyl amines,aryl amines, diaryl amines, triaryl amines, heteroaryl amines,diheteroaryl amines, triheteroaryl amines, heterocyclic amines,diheterocyclic amines, triheterocyclic amines, mixed di- and tri-amineswhere at least two of the substituents on the amine are different andare selected from the group consisting of alkyl, substituted alkyl,alkenyl, substituted alkenyl, cycloalkyl, substituted cycloalkyl,cycloalkenyl, substituted cycloalkenyl, aryl, heteroaryl, heterocyclic,and the like. Also included are amines where the two or threesubstituents, together with the amino nitrogen, form a heterocyclic orheteroaryl group.

Specific examples of suitable amines include, by way of example only,isopropylamine, trimethyl amine, diethyl amine, tri(iso-propyl) amine,tri(n-propyl) amine, ethanolamine, 2-dimethylaminoethanol, tromethamine,lysine, arginine, histidine, caffeine, procaine, hydrabamine, choline,betaine, ethylenediamine, glucosamine, N-alkylglucamines, theobromine,purines, piperazine, piperidine, morpholine, N-ethylpiperidine, and thelike.

Pharmaceutically acceptable acid addition salts may be prepared frominorganic and organic acids. Salts derived from inorganic acids includehydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid,phosphoric acid, and the like. Salts derived from organic acids includeacetic acid, propionic acid, glycolic acid, pyruvic acid, oxalic acid,malic acid, malonic acid, succinic acid, maleic acid, fumaric acid,tartaric acid, citric acid, benzoic acid, cinnamic acid, mandelic acid,methanesulfonic acid, ethanesulfonic acid, p-toluene-sulfonic acid,salicylic acid, and the like.

As used herein, “pharmaceutically acceptable carrier” or“pharmaceutically acceptable excipient” includes any and all solvents,dispersion media, coatings, antibacterial and antifungal agents,isotonic and absorption delaying agents and the like. The use of suchmedia and agents for pharmaceutically active substances is well known inthe art. Except insofar as any conventional media or agent isincompatible with the active ingredient, its use in the therapeuticcompositions is contemplated. Supplementary active ingredients can alsobe incorporated into the compositions.

The term “compound of Formula I” or “compound of Formula II” is intendedto encompass the compounds of the invention as disclosed, and thepharmaceutically acceptable salts, pharmaceutically acceptable esters,and prodrugs of such compounds. Additionally, the compounds of theinvention may possess one or more asymmetric centers, and can beproduced as a racemic mixture or as individual enantiomers ordiastereoisomers. The number of stereoisomers present in any givencompound of the invention depends upon the number of asymmetric centerspresent (there are 2n stereoisomers possible where n is the number ofasymmetric centers). The individual stereoisomers may be obtained byresolving a racemic or non-racemic mixture of an intermediate at someappropriate stage of the synthesis, or by resolution of the compound ofFormula I or Formula II by conventional means. The individualstereoisomers (including individual enantiomers and diastereoisomers) aswell as racemic and non-racemic mixtures of stereoisomers areencompassed within the scope of the present invention, all of which areintended to be depicted by the structures of this specification unlessotherwise specifically indicated.

-   “Isomers” are different compounds that have the same molecular    formula.-   “Stereoisomers” are isomers that differ only in the way the atoms    are arranged in space.-   “Enantiomers” are a pair of stereoisomers that are    non-superimposable mirror images of each other. A 1:1 mixture of a    pair of enantiomers is a “racemic” mixture. The term “(±)” is used    to designate a racemic mixture where appropriate.-   “Diastereoisomers” are stereoisomers that have at least two    asymmetric atoms, but which are not mirror-images of each other.    The absolute stereochemistry is specified according to the    Cahn-Ingold-Prelog R-S system. When the compound is a pure    enantiomer the stereochemistry at each chiral carbon may be    specified by either R or S. Resolved compounds whose absolute    configuration is unknown are designated (+) or (−) depending on the    direction (dextro- or laevorotary) which they rotate the plane of    polarized light at the wavelength of the sodium D line.

Pharmaceutical Compositions

The two components of the invention, an A₁-adenosine receptor agonistand a beta-blocker, calcium channel blocker, or a cardiac glycoside, maybe administered as a pharmaceutical composition that contains a physicalmixture of the two components, but is preferably administered as twoseparate pharmaceutical compositions. Such separate compositions arepreferably administered concurrently, but may also be administered atdifferent times. This invention therefore provides pharmaceuticalcompositions that contain, as the active ingredient, one or two of thecomponents, or a pharmaceutically acceptable salt or ester thereof, andone or more pharmaceutically acceptable excipients, carriers, includinginert solid diluents and fillers, diluents, including sterile aqueoussolution and various organic solvents, permeation enhancers,solubilizers and adjuvants. Such compositions are prepared in a mannerwell known in the pharmaceutical art (see, e.g., Remington'sPharmaceutical Sciences, Mace Publishing Co., Philadelphia, Pa. 17^(th)Ed. (1985) and “Modern Pharmaceutics”, Marcel Dekker, Inc. 3^(rd) Ed.(G. S. Banker & C. T. Rhodes, Eds.).

Administration

The components may be administered in either single or multiple doses byany of the accepted modes of administration of agents having similarutilities, for example as described in those patents and patentapplications incorporated by reference, including rectal, buccal,intranasal and transdermal routes, by intra-arterial injection,intravenously, intraperitoneally, parenterally, intramuscularly,subcutaneously, orally, topically, as an inhalant, or via an impregnatedor coated device such as a stent, for example, or an artery-insertedcylindrical polymer.

One mode for administration is parental, particularly by injection. Theforms in which the novel compositions of the present invention may beincorporated for administration by injection include aqueous or oilsuspensions, or emulsions, with sesame oil, corn oil, cottonseed oil, orpeanut oil, as well as elixirs, mannitol, dextrose, or a sterile aqueoussolution, and similar pharmaceutical vehicles. Aqueous solutions insaline are also conventionally used for injection, but less preferred inthe context of the present invention. Ethanol, glycerol, propyleneglycol, liquid polyethylene glycol, and the like (and suitable mixturesthereof), cyclodextrin derivatives, and vegetable oils may also beemployed. The proper fluidity can be maintained, for example, by the useof a coating, such as lecithin, by the maintenance of the requiredparticle size in the case of dispersion and by the use of surfactants.The prevention of the action of microorganisms can be brought about byvarious antibacterial and antifungal agents, for example, parabens,chlorobutanol, phenol, sorbic acid, thimerosal, and the like.

Sterile injectable solutions are prepared by incorporating the componentin the required amount in the appropriate solvent with various otheringredients as enumerated above, as required, followed by filteredsterilization. Generally, dispersions are prepared by incorporating thevarious sterilized active ingredients into a sterile vehicle whichcontains the basic dispersion medium and the required other ingredientsfrom those enumerated above. In the case of sterile powders for thepreparation of sterile injectable solutions, the preferred methods ofpreparation are vacuum-drying and freeze-drying techniques which yield apowder of the active ingredient plus any additional desired ingredientfrom a previously sterile-filtered solution thereof.

Oral administration is another route for administration of thecomponents. Administration may be via capsule or enteric coated tablets,or the like. In making the pharmaceutical compositions that include atleast one compound of Formula I or II, the active ingredient is usuallydiluted by an excipient and/or enclosed within such a carrier that canbe in the form of a capsule, sachet, paper or other container. When theexcipient serves as a diluent, in can be a solid, semi-solid, or liquidmaterial (as above), which acts as a vehicle, carrier or medium for theactive ingredient. Thus, the compositions can be in the form of tablets,pills, powders, lozenges, sachets, cachets, elixirs, suspensions,emulsions, solutions, syrups, aerosols (as a solid or in a liquidmedium), ointments containing, for example, up to 10% by weight of theactive compound, soft and hard gelatin capsules, sterile injectablesolutions, and sterile packaged powders.

Some examples of suitable excipients include lactose, dextrose, sucrose,sorbitol, mannitol, starches, gum acacia, calcium phosphate, alginates,tragacanth, gelatin, calcium silicate, microcrystalline cellulose,polyvinylpyrrolidone, cellulose, sterile water, syrup, and methylcellulose. The formulations can additionally include: lubricating agentssuch as talc, magnesium stearate, and mineral oil; wetting agents;emulsifying and suspending agents; preserving agents such as methyl- andpropylhydroxy-benzoates; sweetening agents; and flavoring agents.

The compositions of the invention can be formulated so as to providequick, sustained or delayed release of the active ingredient afteradministration to the patient by employing procedures known in the art.Controlled release drug delivery systems for oral administration includeosmotic pump systems and dissolutional systems containing polymer-coatedreservoirs or drug-polymer matrix formulations. Examples of controlledrelease systems are given in U.S. Pat. Nos. 3,845,770; 4,326,525;4,902,514; and 5,616,345. Another formulation for use in the methods ofthe present invention employs transdermal delivery devices (“patches”).Such transdermal patches may be used to provide continuous ordiscontinuous infusion of the compounds of the present invention incontrolled amounts. The construction and use of transdermal patches forthe delivery of pharmaceutical agents is well known in the art. See,e.g., U.S. Pat. Nos. 5,023,252, 4,992,445 and 5,001,139. Such patchesmay be constructed for continuous, pulsatile, or on demand delivery ofpharmaceutical agents.

The compositions are preferably formulated in a unit dosage form. Theterm “unit dosage forms” refers to physically discrete units suitable asunitary dosages for human subjects and other mammals, each unitcontaining a predetermined quantity of active material calculated toproduce the desired therapeutic effect, in association with a suitablepharmaceutical excipient (e.g., a tablet, capsule, ampoule). Thecompounds of Formula I and II are effective over a wide dosage range andis generally administered in a pharmaceutically effective amount. Itwill be understood, however, that the amount of the compound of FormulaI actually administered will be determined by a physician, in the lightof the relevant circumstances, including the condition to be treated,the chosen route of administration, the actual compound administered andits relative activity, the age, weight, and response of the individualpatient, the severity of the patient's symptoms, and the like.

For preparing solid compositions such as tablets, the principal activeingredient is mixed with a pharmaceutical excipient to form a solidpreformulation composition containing a homogeneous mixture of acompound of the present invention. When referring to thesepreformulation compositions as homogeneous, it is meant that the activeingredient is dispersed evenly throughout the composition so that thecomposition may be readily subdivided into equally effective unit dosageforms such as tablets, pills and capsules.

The tablets or pills of the present invention may be coated or otherwisecompounded to provide a dosage form affording the advantage of prolongedaction, or to protect from the acid conditions of the stomach. Forexample, the tablet or pill can comprise an inner dosage and an outerdosage element, the latter being in the form of an envelope over theformer. The two elements can be separated by an enteric layer thatserves to resist disintegration in the stomach and permit the innerelement to pass intact into the duodenum or to be delayed in release. Avariety of materials can be used for such enteric layers or coatings,such materials including a number of polymeric acids and mixtures ofpolymeric acids with such materials as shellac, cetyl alcohol, andcellulose acetate.

Compositions for inhalation or insufflation include solutions andsuspensions in pharmaceutically acceptable, aqueous or organic solvents,or mixtures thereof, and powders. The liquid or solid compositions maycontain suitable pharmaceutically acceptable excipients as describedsupra. Preferably the compositions are administered by the oral or nasalrespiratory route for local or systemic effect. Compositions inpreferably pharmaceutically acceptable solvents may be nebulized by useof inert gases. Nebulized solutions may be inhaled directly from thenebulizing device or the nebulizing device may be attached to a facemask tent, or intermittent positive pressure breathing machine.Solution, suspension, or powder compositions may be administered,preferably orally or nasally, from devices that deliver the formulationin an appropriate manner.

The following examples are included to demonstrate preferred embodimentsof the invention. It should be appreciated by those of skill in the artthat the techniques disclosed in the examples which follow representtechniques discovered by the inventor to function well in the practiceof the invention, and thus can be considered to constitute preferredmodes for its practice. However, those of skill in the art should, inlight of the present disclosure, appreciate that many changes can bemade in the specific embodiments which are disclosed and still obtain alike or similar result without departing from the spirit and scope ofthe invention.

EXAMPLES

The beta blockers, calcium channel blockers, and cardiac glycosides ofthis invention are well known in the art, and are commerciallyavailable. The compounds of Formula I may be prepared by conventionalmethods, in the manner disclosed in U.S. Pat. No. 5,789,416, the entiredisclosure of which is hereby incorporated by reference. For example,the preferred compound CVT-510 is prepared as follows.

Example 1

A. Preparation of (3-(S)-aminotetrahydrofuranyl)purine riboside

Step 1. Resolution of 3-(S)-aminotetrahydrofuran

A mixture of 3-aminotetrahydrofuran hydrochloride (0.5 GM, 4 mmol) and(S)-(+)-10-camphorsulfonyl chloride (1.1 gm, 4.4 mmol) in pyridine (10ml) was stirred for 4 hours at room temperature and then concentrated.The residue was dissolved in ethyl acetate and washed with 0.5Nhydrochloric acid, followed by sodium bicarbonate and then brine. Theorganic layer was dried over magnesium sulfate, filtered, and solventremoved from the filtrate under reduced pressure to provide 1.17 g of abrown oil, which was chromatographed on silica gel (25% to 70% ethylacetate/hexanes). The white solid obtained was repeatedly recrystallizedfrom acetone to yield the (S)-camphorsulfonate of3-(S)-aminotetrahydrofuran.

Step 2. Preparation of 3-(S)-aminotetrahydrofuran hydrochloride

The (S)-camphorsulfonate of 3-(S)-aminotetrahydrofuran (170 mg, 0.56mmol) was dissolved in concentrated hydrochloric acid/acetic acid (2 mLeach), and stirred for 20 hours at room temperature. The reactionmixture was washed three times with methylene chloride (10 ml), and thecombined extracts concentrated to dryness under reduced pressure, togive 75 mg of 3-(S)-aminotetrahydrofuran, as a white solid.

Step 3. Preparation of 6-(3-(S)-aminotetrahydrofuranyl)purine riboside

A mixture of 6-chloropurine riboside (30 mg, 0.10 mmol),3-(S)-aminotetrahydrofuran hydrochloride (19 mg, 0.15 mmol), andtriethylamine (45 ml, 0.32 mmol) in methanol (0.5 ml) was heated to 80°C. for 18 hours. The mixture was cooled, concentrated andchromatographed with 95/5 (methylene chloride/methanol), to give 8 mg of6-(3-(S)-aminotetrahydrofuranyl)purine riboside, as a white solid.

B. Preparation of (3-(R)-aminotetrahydrofuranyl)purine riboside(CVT-510)

Similarly, following steps 1–3 above, but replacing(S)-(+)-10-camphorsulfonyl chloride with (R)-(−)-10-camphorsulfonylchloride, the following compound was prepared:

-   6-(3-(R)-aminotetrahydrofuranyl)purine riboside (CVT-510).

Similarly, other enantiomers of the compounds of Formula I are prepared.

The compounds of Formula II may be prepared by conventional methods, inthe manner disclosed in U.S. patent application Ser. No. 10/194,335, theentire disclosure of which is hereby incorporated by reference. Forexample, the preferred compound CVT-3619 is prepared as follows.

Example 2 Preparation of6-(6-Chloropurine-9-yl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3dioxol-4-yl]methanol

To a solution of2-(6-chloropurin-9-yl)-5-hydroxymethyltetrahydrofuran-3,4-diol (acompound of formula (1)) (4.9 g, 17.1 mmol) and 2,2-dimethoxypropane(10.5 mL, 84.7 mmol) in dimethylformamide (100 mL) was addedp-toluenesulfonic acid (325 mg, 1.71 mmol). After stirring for 24 hoursat 70° C., the reaction was concentrated in vacuo and the residuepurified by flash column chromatography (70%EtOAc/Hexanes) to give6-(6-chloropurine-9-yl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl]methanol,a compound of formula (2), as an off-white solid (2). (3.8 g, 68%) ¹HNMR (CDCl3) δ 1.4 (s, 3H), 1.65 (s, 3H), 3.8–4.0 (dd, 2H), 4.6 (s, 1H),5.1–5.3(m, 2H), 6.0(d, 1H), 8.25(s, 1H), 8.8(s, 1H).

Example 3 Preparation of1-{[(2S,1R,4R,5R)-4-(6-chloropurin-9-yl)-7,7-dimethyl-3,6,8-trioxabicyclo[3.3.0]oct-2-yl]methylthio}-2-fluorobenzene

To a solution of6-(6-chloropurine-9-yl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl]methanol,a compound of formula (2) (0.48 g, 1.47 mmoles) in 20 mL oftetrahydrofuran was added triphenylphosphine (0.77 g, 2.94 mmoles) anddiethylazodicarboxylate (0.47 mL, 2.94 mmoles), and the mixture stirredfor 5 minutes. 2-Fluorothiophenol (0.31 mL, 2.94 mmoles) was then added,and the mixture was stirred under reflux. After 72 hours of reflux, thereaction was concentrated in vacuo and the residue purified by flashcolumn chromatography (20%EtOAc/Hexanes) to give1-{[(2S,1R,4R,5R)-4-(6-chloropurin-9-yl)-7,7-dimethyl-3,6,8-trioxabicyclo[3.3.0]oct-2-yl]methylthio}-2-fluorobenzene,a compound of formula (3), as a clear viscous oil (3). (0.25 g, ˜40%) ¹HNMR (CDCl3) δ 1.4 (s, 3H), 1.6 (s, 3H), 3.2 (m, 2H), 4.6 (t, 1H), 5.1(m, 1H), 5.5 (m, 1H), 6.0 (d, 1H), 7.0 (m, 2H), 7.2 (m, 1H), 7.4 (m,1H), 8.25 (s, 1H), 8.75 (s, 1H).

Example 4 Preparation of(9-{(4S,1R,2R,5R)-4-[(2-fluorophenylthio)methyl]-7,7-dimethyl-3,6,8-trioxabicyclo[3.3.0]oct-2-yl}purin-6-yl)cyclopentylamine

To a solution of1-{[(2S,1R,4R,5R)-4-(6-chloropurin-9-yl)-7,7-dimethyl-3,6,8-trioxabicyclo[3.3.0]oct-2-yl]methylthio}-2-fluorobenzene,a compound of formula (3), (0.125 g, 2.86 mmoles) in 10 mL of ethanoland 1 mL of triethylamine was added cyclopentylamine in excess, and themixture refluxed under nitrogen for 24 hours. The solvent was removedunder reduced pressure, and the residue was purified by preparative TLCusing 1:1 EtOAc:Hexanes to give(9-{(4S,1R,2R,5R)-4-[(2-fluorophenylthio)methyl]-7,7-dimethyl-3,6,8-trioxabicyclo[3.3.0]oct-2-yl}purin-6-yl)cyclopentylamine,a compound of formula (4), as a yellow oil (80 mg, 56%) ¹H NMR (CDCl3) δ1.4 (s, 3H), 1.6 (s, 3H), 1.6–2.4 (m, 6H), 3.15–3.25 (m, 2H), (bs, 1H),4.4)1H), (t, 1H), 5.1 (m, 1H), 5.5 (m, 1H), 6.0 (d, 1H), 6.2 (bs, 1H),7.0 (m, 2H), 7.2 (m, 1H), 7.4 (m, 1H), 7.8 (s, 1H), 8.25 (s, 1H).

Example 5 Preparation of(4S,5S,3R)-2-[6-(cyclopentylamino)purin-9-yl]-5-[(2-fluorophenylthio)methyl]oxolane-3,4-diol

(9-{(4S,1R,2R,5R)-4-[(2-fluorophenylthio)methyl]-7,7-dimethyl-3,6,8-trioxabicyclo[3.3.0]oct-2-yl}purin-6-yl)cyclopentylamine,a compound of formula (4) (50 mg) was dissolved in a mixture of aceticacid (8 mL) and water (2 mL) and heated at 90 C for 16 hours. Solventswere removed under reduced pressure, and the residue was purified bypreparative TLC [methanol-dichloromethane(1:9)] to afford(4S,5S,3R)-2-[6-(cyclopentylamino)purin-9-yl]-5-[(2-fluorophenylthio)methyl]oxolane-3,4-diol,a compound of Formula I, ¹H NMR (CDCl3) δ 1.6–2.4 (m, 6H), 3.15–3.25 (m,2H), 4.1 (bs, 1H), 4.4–4.65 (m, 4H), 6.0 (d, 1H), 6.8 (bs, 1H), 7.05 (m,2H), 7.2 (m, 1H), 7.8 (s, 1H), 8.25 (s, 1H).

EXAMPLE 6 Studies in Awake Rats

Methods

Rats (Sprague Dawley) weighing 300–400 gms were purchased from Simonsenlaboratories. CVT-3619 was dissolved in DMSO and further diluted insaline. CVT-510 was dissolved in saline. Ketamine was purchased fromFort Dodge Animal Health, Xylazine from Bayer and Acepromazine Maleatefrom Fermenta Animal Health Co. Metoprolol and propranolol werepurchased from SIGMA. Esmolol was obtained from a local pharmacy.

Telemetry Studies

For these studies, rats were instrumented with radiotelemeteredtransmitters (Data Sciences) at least 3 weeks prior to experimentation.Animals were anesthetized by peritoneal injection of a “cocktail” (1ml/kg) containing Ketamine (75 mg/ml), Xylazine (5 mg/ml), andAcepromazine (1 mg/ml). After 20–30 minutes of induction of anesthesia,a midline laparotomy was performed. The transmitter for recordings ofECG, blood pressure and body temperature was placed in the abdominalcavity, and secured to the abdominal muscles. Two electrocardiographicleads were tunneled through the subcutaneous—one toward the upper leftshoulder and the other to the right thigh, and secured with sutures. Afluid filled sensor catheter was inserted in the descending aorta abovethe iliac bifurcation for measurement of blood pressure. The tip of thetelemetry catheter was located in the abdominal aorta just caudal to therenal arteries. Once the transmitter and leads were in place anddetermined to be functioning properly, the abdominal wall was sutured.After recovery from anesthesia, the rats were housed individually incages placed on their respective receivers. The ECG, blood pressure andtemperature were recorded and heart rate measured by a Dataquest ARTGold system (Version 2.2; Data Sciences Intl). The system consisted of atransmitter, i.e., biopotential sensor (Model TL11M2-C50-PXT), receivers(Model RPC-1), a consolidation matrix (BCM 100), a personal computer(Compaq DeskPro Series 3574) and Dataquest 4 software. Heart rate, bloodpressure and temperature were measured at 5-minute intervals. Eachrecording lasted 10 seconds and all cardiac cycles within this periodwere averaged. Animals were given various drugs in a randomized mannerafter recording the baseline data for at least two hours.

Implantation of Osmotic Pump

A subgroup of animals was implanted with osmotic pumps containingCVT-510 for combination experiments. After 7 days or more of having beenimplanted with radio-telemetry transmitters for recording ECG (L-2), andverifying that the transmitters were functioning, each rat was implantedwith an Alzet mini-osmotic pump. Under anesthesia (see above) andsterile conditions, one Alzet mini-osmotic pump, was implantedsubcutaneously (SC) in the interscapular area of each rat. The osmoticpumps were filled with either vehicle or CVT-510 (to deliver a dose of20 μg/kg/hr).

Surgical Insertion of Catheters for Determining Plasma Concentrations

Carotid artery was catheterized to obtain serial blood samples for theanalysis of CVT-510 plasma concentrations. Animals were anesthetized byperitoneal injection of a “cocktail” (1 ml/kg) containing Ketamine (75mg/ml), Xylazine (5 mg/ml), and Acepromazine (1 mg/ml). After a 20–30min. of induction of anesthesia, a midline incision was made in the neckregion to expose the external carotid artery. A tunnel is made for thecatheter using blunt dissection in the subcutaneous pocket on the dorsalsection of the neck where it is externalized. The carotid artery wascannulated with 24-gauge catheters sampling of blood for determinationof plasma levels of CVT-510. Externally, the catheter is tied at theback of the neck and a piece of suture is tied around the knot leavingboth ends about 2 inches long for retrieval from under the skin. Theknotted catheter is retracted back under the skin to prevent beingpulled out by the rat. The incision is then cleaned with saline, closedwith wound clips, and an antibiotic (0.4 ml of a 40 mg/ml solution ofgentamicin) is given I.V. Animals were allowed to recover for at least48 hrs before performing the experiment. On the day of the experiment,an injection plug was attached to a 19-gauge IV set, filled with 0.1%heparinized saline and the needle end was inserted into the catheters.Animals were given either a saline or metoprolol injection 1 hr prior toCVT-510 injection. About 400 μl of blood was drawn from the line in thecarotid artery and 400 ul saline flushed in to replace blood volume atpredetermined time points. Plasma was separated and saved at −80° C. foranalysis of CVT-510 levels.

Determination of Plasma Concentrations of CVT-510

CVT-510 plasma level analysis was performed as follows. Briefly, 50 μLof plasma sample was precipitated with 400 μL of acetonitrile:methanol(90:10) containing internal standard. The filtrates were evaporated todryness and reconstituted in 100 μL of 90:10 water:methanol.Concentration of CVT-510 in protein precipitation filtrates wereanalyzed by LC-MS-MS using a Waters Alliance 2690 HPLC system (Millford,Mass.) coupled to a Waters/Micromass Quattro Ultima triple quadrupolemass spectrometer (Millford, Mass.). Calibration curves were constructedby plotting peak area ratios of the analyte to internal standard againstconcentration, using a weighted (1/X) linear regression model in allinstances.

Data Analysis

The slowing of heart rate caused by each treatment was quantified bydetermining the area under the curve (AUC), using the trapezoidal methodfor calculations. Data used for analysis was the area under/over thecurve calculated using change form baseline data (untreated animals).The data was analyzed for the magnitude as well as the duration ofbradycardia caused by each treatment. The AUC values for various dosesfor each monotherapy were compared using one-way ANOVA followed byTukey's test for multiple comparisons. The significance level was set atp<0.05 for all comparisons.

The results obtained from the above studies are shown in Figure form, asfollows.

-   FIG. 1 shows the effect of CVT-3619 (a partial A₁ receptor agonist)    on heart rate with and without propranolol in awake rats    instrumented with telemetry radiotransmitters. CVT-3619 at dose of    (0.5 mg/kg, ip) by itself had minimal effect on heart rate. However    when given in the presence of a beta blocker (propranolol, 10 mg/kg,    ip), there is significant lowering of heart rate below baseline as    compared to CVT-3619 alone. Propranolol was given 10 minutes prior    to CVT-3619 injection.-   FIG. 2 shows the summary of data obtained from telemeterized awake    rats. The data was quantified as area under the curve (AUC) and    presented as a decrease in total number of heart beats for a 2 hour    period of time caused by CVT-3619 (given ip) alone at two different    doses and in the presence of propranolol (10 mg/kg, ip given 10    minutes prior to CVT-3619). The combination of CVT-3619 and    propranolol results in a synergistic effect on heart rate, as the    effect observed with combination is much greater than the calculated    sum of the effect of each agent.-   FIG. 3 shows the effect of CVT-510 and esmolol alone and given    together as a mixture via ip injection to awake rats instrumented    with telemetry radiotransmitters. CVT-510 at 20 μg/kg dose    transiently lowers the heart rate below baseline levels whereas    esmolol (10 mg/kg ip) only slightly reduces the increase in heart    rate (which is caused caused by handling the animal). When the two    agents are given in combination, the effect on heart rate is much    greater. The combination not only increases the magnitude of the    response but also increases the duration of bradycardia    significantly.-   FIG. 4 shows the effect of CVT-510 alone and the effect when    combined with the beta-blocker, Metoprolol, by observing the effect    on heart rate in awake rats instrumented with telemetry    radiotransmitters. CVT-510 (20 μg/kg, ip) slowed the heart rate in a    dose dependent manner. In the presence of Metoprolol (3 mg/kg, ip),    there was a greater lowering of heart rate.-   FIG. 5. The duration of bradycardia caused by CVT-510 was analyzed    by observing the time for the heart rate to return to 90% of    pretreatment levels. In addition to the increase in magnitude of    bradycardia, the combination of CVT-510 and metoprolol resulted in a    significant increase in the duration of bradycardia as compared to    that caused by CVT-510 alone.-   FIG. 6: Plasma levels of CVT-510 were determined in the absence and    presence of metoprolol in a separate group of animals (FIG. 6).    Plasma levels of CVT-510 were found to be similar in both groups    even though the slowing of heart rate caused by CVT-510 was greater    in the presence of metoprolol indicating that the metabolism of    CVT-510 was not changed in the presence of metoprolol.-   FIG. 7: To further investigate the mechanism of interaction of    CVT-510 and beta-blockers, another series of experiments were    performed in which the dose of CVT-510 was kept constant while the    dose of metoprolol was varied. First a full dose response curve for    metoprolol (0.1–10 mg/kg, ip) alone was obtained (FIG. 7, ▪    symbols). In the second phase of the study, animals were implanted    with osmotic pumps subcutaneously containing CVT-510. CVT-510 was    delivered at a rate of 20 μg/kg/hr, which yielded plasma    concentration of 7.5±1 ng/ml. Metoprolol dose response curve was    repeated in these animals. In the presence of CVT-510, metoprolol    dose response curve was shifted to the left and downward (FIG. 7, •    symbols).-   FIG. 8: This figure represents the data shown in FIG. 7. The slowing    of heart rate caused by CVT-510 and metoprolol was quantified by    determining the area under the curve (AUC) for a period of 60 min    for each treatment. The combined effect of CVT-510 and metoprolol on    heart rate was found to be synergistic.-   FIGS. 9–10: Studies in Anesthetized Guinea Pigs.

Male guinea pigs weighing 400–450 gm were obtained from Simonsen labsand housed in the institutional laboratory animal facility. Animals wereanesthetized with isoflurane in the anesthetizing chamber. Afterdetermining (by toe pinch) that the animal is adequately anesthetized,the animals was intubated with an endotracheal tube and ventilated withisoflurane and oxygen mixture using anesthesia workstation. Usingsterile equipment and aseptic technique, the right carotid artery wasexposed and a catheter inserted for recording of blood pressure (BP). Aquadripolar electrode catheter was introduced via the right jugular veinand positioned in the right atrium and ventricle for atrial andventricular pacing. The hearts were paced at a constant rate (330–360bpm) to eliminate the effect of heart rate variability between animals.Another catheter was inserted into the left jugular vein and positionedin the right atrium for the administration of drugs and saline.Subcutaneous needles were used as standard electrocardiographic leads torecord the electrocardiogram (ECG). After completion of surgery andinstrumentation, a 20 min equilibration period was allowed beforebeginning the experimental protocol. The data was recorded using PowerLab data acquisition system.

-   FIG. 9: CVT-510 (0.5 μg/kg) and metoprolol (0.1 mg/kg), which were    given as an iv bolus, demonstrated an increased PR interval by 5    msec each in anesthetized guinea pigs. When the two agents were    given in combination the PR interval was increased up to 15 msec.    This is a synergistic effect, as the observed effect is more than    the algebraic sum of the effect of each agent.-   FIG. 10: Similar results were obtained when CVT-510 was given in the    presence of with another beta-blocker, esmolol. Esmolol was    administered at three different infusion rates. CVT-510 was given 15    minutes after starting the infusion of Esmolol. Effect of CVT-510 on    PR interval was increased with increasing doses of esmolol. The    duration of effect was significantly prolonged in a dose-dependent    manner.

Thus, it has been demonstrated that the combination of a beta-blockerand A₁ agonist results in synergistic effects on heart rate in rats andPR interval in guinea pigs. The combined effect is dependent on the doseof either agent. That is, one can achieve similar responses by keepingone agent constant and varying the other. Various routes ofadministration of the drugs have been tried, and different combinations.For example, one drug has been administered 10 minutes afteradministration of the first, and 1 hour after administration of thefirst. The drugs have been given as a mixture, or given separately atthe same time. The response varies in magnitude, but the overall effectis same. It has also been demonstrated that the combination is effectiveusing both full A₁ adenosine receptor agonists and partial A₁ adenosinereceptor agonists.

The combination has been shown to be effective in two different models.

-   1) Measurement of heart rate in awake rats, which is not a target    for the A₁ agonists, but is used as a surrogate for the effect of A₁    agonists. The advantage of this model is that the high sympathetic    tone seen in many forms of arrhythmias is simulated.-   2) In anesthetized guinea pigs the AV nodal conduction method is    useful for measuring the PR interval, which is the target of A₁    agonists. However, the sympathetic tone is blunted in this model due    to anesthesia.

base- CVT-510 Alone (μg/kg) base- DIGOXIN + CVT-510 (μg/kg) Animal #line 1.69 2.53 3.37 8.43 16.85 line 1.69 2.53 3.37 8.43 16.85 digoxin#150 70 100 100 160 50 90 80 90 140 digoxin#2 30 40 50 60 110 50 60 70 80100 digoxin#3 40 50 50 70 100 140 50 90 100 100 100 160 digoxin#4 60 90120 120 120 140 60 90 120 140 130 150 digoxin#5 40 60 70 100 150 100 60120 120 120 100 90 n 5 5 4 5 4 5 5 5 5 5 3 5 MEAN 44 62 73 90 118 130 5490 98 106 110 128 SD 11 19 33 24 24 24 5 21 23 24 17 31 SEM 5 9 17 11 1211 2 9 10 11 10 14 base- CVT-510 Alone (μg/kg) base- ESMOLOL + CVT-510(μg/kg) Animal # line 1.69 2.53 3.37 8.43 16.85 line 1.69 2.53 3.37 8.4316.85 esmolol#1 40 60 60 100 100 110 60 80 90 100 100 100 esmolol#2 3040 60 60 80 100 50 60 60 90 90 140 esmolol#3 50 80 90 120 140 140 50 80130 120 140 esmolol#4 30 40 50 70 90 90 40 50 50 70 80 80 esmolol#5 4090 90 100 110 100 50 90 120 100 130 130 n 5 5 5 5 5 5 5 5 5 5 5 4 MEAN38 62 70 90 104 108 50 72 90 96 108 113 SD 8 23 19 24 23 19 7 16 35 1826 28 SEM 4 10 8 11 10 9 3 7 16 8 12 14 base- CVT-510 Alone (μg/kg)base- IBUTILIDE + 510 (μg/kg) Animal # line 1.69 2.53 3.37 8.43 16.85line 1.69 2.53 3.37 8.43 16.85 ibutilide#1 35 40 45 60 80 140 40 80 9090 80 ibutilide#2 70 90 150 150 150 160 75 110 110 130 120 110ibutilide#3 40 40 50 55 70 75 50 60 70 70 70 70 ibutilide#4 40 60 70 90100 80 50 70 80 90 90 120 ibutilide#5 40 45 50 55 80 90 50 60 65 70 9080 n 5 5 5 5 5 5 5 5 5 5 5 4 MEAN 45 55 73 82 96 109 53 76 83 90 90 95SD 14 21 44 41 32 38 13 21 18 24 19 24 SEM 6 9 20 18 14 17 6 9 8 11 8 12base- CVT-510 Alone (μg/kg) base- QUINIDINE + CVT-510 (μg/kg) Animal #line 1.69 2.53 3.37 8.43 16.85 line 1.69 2.53 3.37 8.43 16.85quinidine#1 40 50 55 60 90 90 50 70 70 70 105 125 quinidine#2 30 40 4545 100 100 50 70 70 65 90 130 quinidine#3 40 60 65 70 110 110 70 80 8595 115 120 quinidine#4 40 50 90 110 130 120 60 75 115 115 120 95quinidine#5 50 50 60 70 80 70 40 60 95 100 90 105 N 5 5 5 5 5 5 5 5 5 55 5 MEAN 40 50 63 71 102 98 54 71 87 89 104 115 SD 7 7 17 24 19 19 11 719 21 14 15 SEM 3 3 8 11 9 9 5 3 8 9 6 7 PROCAINAMIDE + base- CVT-510Alone (μg/kg) base- CVT-510 (μg/kg) Animal # line 1.69 2.53 3.37 8.4316.85 line 1.69 2.53 3.37 8.43 16.85 procanimide#1 45 50 60 65 95 85 6565 70 80 90 110 procanimide#2 50 55 70 95 105 105 55 80 110 120 120 120procanimide#3 40 50 80 95 95 110 55 65 105 110 110 110 procanimide#4 4050 55 65 75 75 65 50 80 90 90 90 procanimide#5 45 55 65 80 90 100 50 8085 85 85 85 n 5 5 5 5 5 5 5 5 5 5 5 5 MEAN 44 52 66 80 92 95 58 68 90 9799 103 SD 4 3 10 15 11 15 7 13 17 17 15 15 SEM 2 1 4 7 5 7 3 6 8 8 7 7base- CVT-510 Alone (μg/kg) base- ATONOLOL + CVT-510 (μg/kg) Animal #line 1.69 2.53 3.37 8.43 16.85 line 1.69 2.53 3.37 8.43 16.85 atonolol#250 70 100 180 120 120 70 120 170 180 180 220 atonolol#3 45 80 100 120120 120 60 130 150 180 180 180 atonolol#4 45 50 50 75 100 85 45 60 90110 125 130 atonolol#5 45 50 70 90 130 165 50 120 160 130 160 160atonolol#6 40 50 110 115 120 120 50 65 120 120 120 210 n 5 5 5 5 5 5 5 55 5 5 5 MEAN 45 60 86 116 118 122 55 99 138 144 153 180 SD 4 14 25 40 1128 10 34 33 34 29 37 SEM 2 6 11 18 5 13 4 15 15 15 13 16 base- CVT-510Alone (μg/kg) base- SOTALOL + CVT-510 (μg/kg) Animal # line 1.69 2.533.37 8.43 16.85 line 1.69 2.53 3.37 8.43 16.85 sotalol#1 40 70 110 140140 140 60 90 140 140 140 180 sotalol#2 40 55 100 110 130 140 60 130 140140 140 140 sotalol#3 55 60 70 80 85 130 65 85 115 110 130 190 sotalol#440 45 50 50 70 105 60 90 85 100 100 105 sotalol#5 40 50 110 115 120 12070 65 120 120 120 210 n 5 5 5 5 5 5 5 5 5 5 5 5 MEAN 43 56 88 99 109 12763 92 120 122 126 165 SD 7 10 27 35 30 15 4 24 23 18 17 42 SEM 3 4 12 1613 7 2 11 10 8 7 19

1. A method of treating arrhythmias in a mammal, comprisingadministration of a synergistic therapeutically effective minimal doseof an A₁ adenosine receptor agonist in conjunction with atherapeutically effective minimal dose of a beta blocker, calciumchannel blocker, or cardiac glycoside, to a mammal in need thereof. 2.The method of claim 1, wherein the A₁ adenosine receptor agonist is acompound of Formula I:

wherein R₁ is an optionally substituted heterocyclic group.
 3. Themethod of claim 2, wherein the compound of Formula I is administered inconjunction with a therapeutically effective minimal dose of a betablocker.
 4. The method of claim 3, wherein in Formula I R¹ is3-tetrahydrofuranyl, 3-tetrahydrothiofuranyl, 4-pyranyl, or4-thiopyranyl.
 5. The method of claim 4, wherein the beta blocker isatenolol, esmolol, sotalol, metoprolol, or propranolol.
 6. The method ofclaim 5, wherein the compound of Formula I R¹ is6-(3-(R)-N-aminotetrahydrofuranyl)purine riboside, namely CVT-510. 7.The method of claim 6, wherein CVT-510 is present in an amount fromabout 0.0001–0.05 mg/kg.
 8. The method of claim 6, wherein the betablocker is present in an amount from about 0.01 to 200 mg/kg.
 9. Themethod of claim 8, wherein the beta blocker is esmolol.
 10. The methodof claim 9, wherein CVT-510 is present in an amount from about0.0005–0.020 mg/kg and esmolol is present in an amount from about 0.1 to10 mg/kg.
 11. The method of claim 1, wherein the A₁ adenosine receptoragonist is a compound of Formula II:

wherein: R¹ is optionally substituted alkyl, optionally substitutedcycloalkyl, optionally substituted aryl, or optionally substitutedheteroaryl; R² is hydrogen, halo, trifluoromethyl, optionallysubstituted acyl, or cyano; R³ is optionally substituted alkyl,optionally substituted cycloalkyl, optionally substituted aryl;optionally substituted heteroaryl, or optionally substitutedheterocyclyl, R⁴ and R⁵ are independently hydrogen or optionallysubstituted acyl; and X and Y are independently a covalent bond oroptionally substituted alkylene.
 12. The method of claim 11, wherein thecompound of Formula II is administered in conjunction with atherapeutically effective minimal dose of a beta blocker.
 13. The methodof claim 12, wherein the beta blocker is atenolol, esmolol, sotalol,metoprolol, or propranolol.
 14. The method of claim 13, wherein R¹ is(R)-2-hydroxycyclopentyl, X and Y are covalent bonds, R², R³, and R⁴ arehydrogen, and R⁵ is 2-fluorophenyl, namely2-{6-[((1R,2R)-2-hydroxycyclopentyl)amino]purin-9-yl}(4S,5S,3R)-5-[(2-fluorophenylthio)methyl]oxolane-3,4-diol(CVT-3619).
 15. The method of claim 14, wherein CVT-3619 is present inan amount from about 0.1 to 200 mg/kg.
 16. The method of claim 14,wherein the beta blocker is present in an amount from about 0.01 to 100mg/kg.
 17. The method of claim 16, wherein the beta blocker is esmolol.18. The method of claim 17, wherein CVT-3619 is present in an amountfrom about 0.5 to 50 mg/kg and esmolol is present in an amount fromabout 0.1 to 10 mg/kg.